The present invention relates to a red light emitting long afterglow photoluminescence phosphor which emits light being excited by visible rays and ultraviolet rays, and an afterglow lamp coated with this phosphor. More specifically, the present invention relates to the red light emitting long afterglow photoluminescence phosphor which is a rare earth oxysulfide phosphor activated by Europium and coactivated by a specified element, and an afterglow lamp coated with this phosphor.
Phosphors, which are irradiated by the light from sunlight and from artificial lighting, and also phosphors, which exhibit afterglow for a relatively long time in dark places, are among phosphors, which are called light storing phosphors because this phenomenon can be repeated several times. Nowadays, with the ever-increasing complications of life, interest in disaster prevention has increased. Particularly the use of light storing phosphors afterglowing in dark places for disaster prevention has become progressively greater. Furthermore, the mixing of light storing phosphors into plastic allows the making of plates, sheets or the like, broadening their use in many fields.
The conventional substances used green light emitting ZnS: Cu phosphor as a light storing phosphor, but it did not provide sufficient performance. This is because this phosphor has the following intrinsic drawbacks. One is the phosphorescent luminance (luminance of the afterglow) which is not high enough to be found within several tens of hours. Another is the dark coloration of the surface due to the precipitation of colloidal metallic zinc on the surface of the crystal of the phosphor because of the decomposition due to the ultraviolet, the problem being a severe reduction or deterioration of the phosphorescent luminance. This deterioration accelerates particularly under the conditions of high temperature and humidity and usually, to ameliorate this drawback, a light proof treatment is applied on the surface of the ZnS:Cu phosphor, but the complete prevention still remains difficult. For this reason, the use of the ZnS:Cu phosphor has to be avoided in external places directly exposed to the sun""s rays.
In this connection, a purplish-blue to green light emitting light storing phosphor in which the main crystals are comprised of a chemical compound represented by MAl2O4 activated by divalent Europium in which M is comprised of at least one metallic element selected from the group consisting of Ca, Sr, Ba, has been disclosed in Japanese Non-examined Patent Publication No. 7-11250 issued in 1995. According to this publication, the phosphor is considered to have solved the intrinsic drawbacks of the here above-mentioned zinc sulfide phosphor. Furthermore, the main component of this phosphor has already been disclosed in U.S. Pat. No. 2,392,814, and in U.S. Pat. No. 3,294,699.
A blue-green light emitting long afterglow phosphor has been disclosed in the Japanese Non-examined Patent Publication No. 8-170076 issued in 1996 in which chemical compound is represented by MO.a(All-bBb)2O3:cR in which MO is at least one of divalent metallic oxides selected from the group consisting of MgO, CaO, SrO, and ZnO R is at least one of rare earth element selected from the group consisting of Pr, Nd, Dy, and Tm.
The long afterglow light storing phosphor of this type emitting purplish-blue to green light, have been much studied and are presently used, but among light storing phosphors emitting red light, are only known CaS:Eu, Tm which have short afterglow properties and a poor chemical stability. Where the phosphors are used such as decoration purpose, because a variety of tones of afterglow are necessary, the achievement of a chemically stable and long afterglow red light emitting long afterglow photo-luminescence phosphor has been needed. The hereabove long afterglow means the phosphorescence of photoluminescence with long afterglow time.
Furthermore, as phosphor excited by electron rays, a phosphor of rare earth oxysulfide exited by Europium has been developed and is used as the cathode ray tube being the cathode luminescence phosphor. But, because electron rays excite this phosphor, it has been rarely studied as photoluminescence phosphor excited by ultraviolet rays.
The inventors, by further improving this phosphor, have succeeded in developing a red light emitting long afterglow photoluminescence phosphor with fairly long afterglow properties. Therefore the first object of the present invention is to offer a red light emitting long afterglow photoluminescence phosphor excited by ultraviolet rays or the like, not by electron rays.
Incidentally, the purplish-blue to green light emitting light storing phosphors with long afterglow, have already been developed and are used for afterglow type lamps or the like, such as guide lamps.
Guide lamps are required to be installed at places where many people gather, such as theaters or hotels, by fire regulations in each city. In case of disasters such as an earthquake or a fire, or other accident, commercial power sources are shut down and it is assumed that backup power sources automatically switch on to turn such emergency guide lamps on for least 20 minutes. However, if the backup power sources were broken or their circuits were cut by the disaster, the guide lamps would turn off. In such cases, a complex underground street, a long tunnel, nighttime multistory buildings or the like would become very dangerous. Further, because the conventional guide lamps have a complicated structure, it takes much time and high cost to install them. Therefore, such guide lamps are rarely provided except in places where the laws require them.
Further, guide lamps are needed not only in emergency situations, and if most huge buildings, such as department stores, schools or factories, and regular buildings like stores and houses, are equipped with guide lamps with simple structures and lower costs, this would allow users to see their feet from the time when they turn off the switches on the lights of a room, corridor or staircase, until they reach the exit and, they would be more safe and comfortable.
In this connection, providing a light storing substance capable of absorbing and storing optical energy emitted from a light source on a supporting member, and as a shade positioned within where the light from the light source reaches, has been disclosed in Japanese Non-examined Patent Publication No.58-121088 issued Jul. 19, 1983. By using this light storing substance, backup power sources will not be required. However, the conventional light storing substances are disadvantageous in that they are chemically unstable and are apt to be deteriorated by ultra-violet rays, high temperatures, moisture or the like. Further, the afterglow of these light storing substances is dark and short. Furthermore, sufficient light cannot be obtained by coating a supporting member with a light storing substance.
The second object of the present invention is to offer a long afterglow lamp with a long afterglow without the emergency backup power sources.
In order to solve the above-mentioned problem, the present inventors eventually achieved the present invention, finding out that the problem can be solved by introducing a specific coactivator into the rare earth oxysulfide phosphor activated by Europium, as a result of research to improve long afterglow properties and phosphorescent luminance.
In sum, the red light emitting afterglow photoluminescence phosphor of the present invention comprises a rare earth oxysulfide phosphor which chemical formula includes following ranges:
Ln2O2S:Eux1My
0.00001xe2x89xa6xxe2x89xa60.5
0.00001xe2x89xa6yxe2x89xa60.3
wherein Ln in the chemical formula is at least one member selected from the group consisting of Y, La, Gd and Lu; M is a coactivator which is at least one member selected from the group consisting of Nb, Ta and Ga.
xe2x80x83Ln2O2S:Eux,Mgy,Mxe2x80x2z
0.00001xe2x89xa6xxe2x89xa60.5
0.00001xe2x89xa6yxe2x89xa60.3
0.00001xe2x89xa6zxe2x89xa60.3
wherein Ln in the chemical formula is at least one member""selected from the group consisting of Y, La, Gd and Lu; Mg is a first coactivator; Mxe2x80x2 is a second coactivator which is at least one member selected from the group consisting of Ti, Nb, Ta and Ga.
The activator and the coactivator introduced into the red light emitting long afterglow photoluminescence phosphor of the present invention greatly influence on the phosphorescent luminance. For example, if Ln is Y in the above formula, each value should be adjusted in each range shown below.
The concentration x of activator Eu should be adjusted in the range between equal or more than 0.00001 mol and equal or less than 0.5 mol, per 1 mol of phosphor. This is because if the value is less than 0.00001 mol then the light absorption gets so worse that the phosphorescent luminance reduces, on the other hand, if the value is more than 0.5 mol then concentration quenching occurs and the phosphorescent luminance lowers. More preferable range of x is between 0.00001xe2x89xa6xxe2x89xa60.1, whereby the phosphorescent luminance is much higher within this concentration.
By introducing the coactivator M, the light emission of Eu has an afterglow property. The effective coactivator M is at least one member selected from the group consisting of Nb, Ta and Ga. When the concentration y of the coactivator M is in the range between 0.00001xe2x89xa6yxe2x89xa60.3, the phosphorescent luminance rises. However, if y is less than 0.00001 then the phosphorescent luminance lowers, and if more than 0.3 then the coactivator M tends not to enter into the phosphor as an element and the phosphorescent luminance lowers.
The optimum concentration range of the coactivator M is follows: 0.005xe2x89xa6yxe2x89xa60.1 in the case of Nb, and 0.001xe2x89xa6yxe2x89xa60.2 in the case of Ta or Ga; wherein the phosphorescent luminance remarkably rises within these ranges of concentrations.
If Mg is selected as the first coactivator, it would be greatly effective for improvement of the phosphorescent luminance for synergism by coactivated with at least one member selected from the group consisting of Ti, Nb, Ta, and Ga as the second coactivator Mxe2x80x2. The effective range of increasing the phosphorescent luminance is follows: the concentration y of the first coactivator Mg is within the range between 0.00001xe2x89xa6yxe2x89xa60.3; the concentration z of the second coactivator Mxe2x80x2 is within the range between 0.00001xe2x89xa6zxe2x89xa60.3.
In case the first coactivator M is Mg, the preferable range of the second coactivator Mxe2x80x2 concentration z is follows: 0.0001xe2x89xa6zxe2x89xa60.3 if Mxe2x80x2 is Ti; 0.005xe2x89xa6zxe2x89xa60.1 if Mxe2x80x2 is Nb; 0.001xe2x89xa6zxe2x89xa60.2 if Mxe2x80x2 is either Ta or Ga; whereby the phosphorescent luminance increases considerably.
In case the second coactivator Mxe2x80x2 is either Ti, Nb, Ta or Ga, then the preferable range of the first coactivator Mg concentration y is 0.01xe2x89xa6yxe2x89xa60.2.
The red, light emitting long afterglow photo-luminescence phosphor of the present invention employs metal oxides such as Y2O3, Eu2O3, MgO and TiO2, or chemical compounds, such as carbonates, nitrates, oxalates and hydroxides which can readily become oxides by burning at high temperature as raw materials thereof Because the purity of the raw materials has a strong influence on the phosphorescent luminance, more than 99.9% purity is preferable, and more preferably, 99.99%. To obtain the red light emitting long afterglow photoluminescence phosphor of the present invention, it is necessary to measure these raw materials to the predetermined mol rate, then, further mix them with sulfur and proper flux (such as carbonate of alkaline metal) and then fire them.
The particle diameter of the red light emitting long afterglow photoluminescence phosphor of the present invention influence on the phosphorescent luminance, so preferably it should be controlled its average particle diameter within the range of 5-30 xcexcm. If the average particle diameter is less than 5 xcexcm, then the phosphorescent luminance deteriorates rapidly, or if more than 30 xcexcm, then the phosphorescent luminance decreases depending on the body color of the phosphor. In addition, in case the average particle diameter is over 30 xcexcm, the characteristics of mixing and coating would get worse where it used for decorations, lamps or the like. The most preferable range of the average particle diameter is 10-30 xcexcm, in which the phosphorescent luminance is higher and more stable.
Where the rare earth oxysulfide phosphor activated by Europium, introducing at least one element selected from the group consisting of Nb, Ta and Ga results the red light emitting long afterglow photoluminescence phosphor having long afterglow and chemical stability which could not be achieved by the conventional CaS:Eu,Tm phosphor. Furthermore, higher phosphorescent luminance can be achieved by the combination of coactivators.
The red light emitting long afterglow photoluminescence phosphor of the present invention is applicable to lamps.
There are various types of lamps which excite the afterglow phosphor.
All kinds of lamps which are currently used in practice are applicable to this, for example, incandescent lamps, fluorescent lamps, HID (high-intensity discharge) lamps and halogen lamps. The FIG. 1 shows an inner fluorescent layer 3 and an outer fluorescent layer 4 coated with the afterglow phosphor on the inner surface and/or the outer surface of a transparent glass 2 covering a light emitting section 1 of the lamp. An afterglow reflection sheet having afterglow properties is also achieved by forming an afterglow fluorescent layer 6 on the surface of the reflection sheet 5 for the lamp.
The thickness of the afterglow phosphor layer applied is dependent on the particle size of the afterglow phosphor which is used, in the meantime its preferable range is 5-100 xcexcm. In case the thickness of the afterglow phosphor layer was out of this range, if less than that, then the amount of the applied long afterglow phosphor would be too small to yield afterglow, on the contrary if more than that, the light emitted from the lamp would be interrupted by the afterglow phosphor such that the original function of the lamp as an illuminator would be lowered.
The afterglow lamps are designed as mentioned above. Turning especially to fluorescent lamps, the phosphor of the fluorescent layer on the inner surface of the glass tube is exited by ultraviolet rays and emits light. Therefore it is also possible to use the ultraviolet rays energy directly. Where the afterglow phosphor is applied on the inner surface of the glass tube of fluorescent lamp, the afterglow phosphor is also exited directly by 253.7 nm mercury rays radiated from a positive column that is a light emitting section of a fluorescent lamp. Consequently, another afterglow fluorescent lamp is made by applying the long afterglow phosphor alone on the fluorescent lamp. In this case, the afterglow light is maximum. Nevertheless, since the lamp is used as a common white light fluorescent lamp in normal situation, preferably it should be used in combination with a phosphor for a fluorescent lamp so that it receives the light from this phosphor for the fluorescent lamp and thereby emits afterglow.
For example, an illustration of a structure receiving light from another phosphor is shown in FIG. 2 which is the cross-sectional view perpendicular to the fluorescent lamp tube direction. Energy which is converted from electric energy to optical energy (in this case ultraviolet radiant energy) excites the fluorescent layer 3 formed on the inner surface of a light transmittable glass 2 mainly in the light emitting section 1 of a positive column. In this case it is permissible to mix the afterglow phosphor with an illuminating phosphor, which excites the afterglow phosphor, in the fluorescent layer completely, and it is the easiest way to carry out the invention.
Furthermore, there is a so-called bilayer application, in which is formed an afterglow phosphor layer 6 on the inner surface of the light transmittable glass 2 as the first layer, and an illuminating phosphor layer 7 as the second layer, as shown in the sectional view FIG. 3 of a fluorescent lamp. In this method, a 253.7 nm mercury ray is consumed to excite the phosphor for the fluorescent lamp mostly, and the afterglow phosphor is excited by the visible ray from the phosphor layer mostly. The afterglow lamp obtained here yield high level of luminance for illumination and its afterglow also has a high-intensity.
On the other hand, as shown in the sectional view FIG. 4 of the fluorescent lamp, it is possible to form an illumination phosphor layer 7 on the inner surface of a transparent glass 2, and an afterglow phosphor layer 6 on the outer surface of its glass tube.
A commonly used illumination phosphor is usable as a phosphor used with the afterglow phosphor, which fills the phosphor layer, concurrently. For example, the following are usable: (SrCaBaMg)5(PO4)3Cl:Eu, BaMg2Al16O27:Eu, Sr5(PO4)3Cl:Eu, LaPO4:Ce,Tb, MgAl11O19:Ce,Th, Y2O3:Eu, Y(PV)O4:Eu, 3.5MgOxe2x80x940.5MgF2xe2x80x94GeO2:Mn, Ca10(PO4)6FCl:Sb,Mn, Sr10(PO4)6FCI:Sb,Mn, (SrMg)2P2O7:Eu, Sr2P2O7:Eu, CaWO4:Pb, MgWO4, (BaCa)5(PO4)3Cl:Eu, Sr4Al14O25:Eu, Zn2SiO4:Mn, BaSi2O5:Pb, SrB4O7Eu, (CaZn)3(PO4)2:Ti, LaPO4:Ceb, ect.
Red color emitting phosphors which mainly emit light in wavelength more than 600 nm are not used for exciting the afterglow phosphor. This is because the afterglow phosphor cannot be excited by light emission of such phosphors with long wavelengths. However, the commonly used illuminator fluorescent lamps mostly emit light throughout the visible range. Thus, where having such fluorescent lamps with afterglow property, although red color light is not necessary for the afterglow phosphor, it is still necessary for setting the light color of the fluorescent lamp within a required range.
In view of intensive excitation of afterglow phosphor, white light emitting as the fluorescent lamp illuminator and variable light color of a fluorescent lamp, the most preferable phosphor is the three component type phosphor which comprises a blue light emitting phosphor having a light emission peak around 450 nm wavelength, a green light emitting phosphor having a light emission peak around 545 nm wavelength and a red light emitting phosphor having a light emission peak around 610 nm wavelength. As preferable usage, (SrCaBaMg)5(PO4)3Cl:Eu or BaMg2Al16O27:Eu is suitable for the blue light emitting phosphor, LaPO4:Ce,Tb or MgAl11O19:Ce,Th for the green light emitting phosphor and Y2O3:Eu for the red light emitting phosphor.
The mixing ratio of the afterglow phosphor constituting the fluorescent layer and the phosphor for the fluorescent lamp mixed therewith can be freely changed according to the purpose of the lamp. For example, when the priority is given to the use as an illuminator, i.e., the luminous flux of the lamp is most important, the proportion of the phosphor for the fluorescent lamp is increased. On the contrary, when luminance and long afterglow are required, it can be realized by increasing the proportion of the long afterglow phosphor.
Further, for manufacturing an afterglow fluorescent lamp, a usual method for manufacturing fluorescent lamps can be applied. For example, a long afterglow phosphor, a phosphor which is put together with the long afterglow phosphor for exciting it and a binding agent such as alumina, calcium pyrophosphate or calcium barium borate are added to a nitro cellulose/butyl acetate solution, and are mixed and suspended to prepare a phosphor coating suspension. The obtained phosphor coating suspension is flown on the inner surface of the glass tube of the fluorescent lamp, then dried through hot air blowing. After that fluorescent lamp is completed following the usual manufacturing steps including baking, evacuation, filament fitting, base attachment or the like.
In coating process on the glass tube, it is possible to form a protective layer, such as alumina, then a phosphor layer thereon, whereby the light emitting performance such as the luminous flux or the luminous flux maintenance is further improved.
The above mentioned afterglow lamp can yield a bright afterglow and therefore eliminates an emergency backup power supply.
It is very economical to apply this afterglow fluorescent lamp to a guide lamp, because it makes it possible to apply the existing illumination device, without providing any particular illumination device like coated with a light storing substance. As a result, the cost restriction associated with choosing the places where the guide lamps are provided can be reduced.
Further, even if this afterglow fluorescent lamp is incorporated into a conventional guide lamp having a backup power supply, it is still useful and it ensures a very reliable guide lamp since it can function as a guide lamp even if the backup power supply or other power supplying circuit is cut down by disaster or other events.
In addition, the afterglow fluorescent lamp can serve not only as emergency lamp, but also as an additional lamp furnished in a room, a corridor or a staircase for illuminating one""s feet after one has switched off the light until one reaches an exit, because this afterglow lamp can provide an afterglow of a high luminance for a while after the switch is turned off.